Ireland is the first country to use a national referendum to offer to extend marriage rights to gay couples.
Catholic, Pat Carey, 67, a former Irish government minister in the previous administration, and a 'Yes' vote campaigner who came out as gay himself earlier this year, says it's been an emotional campaign: "This is at the end of the day a referendum which will allow people who wish to get married civilly, to do so.
"It's nothing to do with church marriages, there'll be no restrictions on churches or how they solemnize marriages or anything like that," he told Premier's News Hour.
However, John Waters, a 'No' campaigner and Sunday Independent columnist believes what the family means in the eyes of the state is being fundamentally changed: "The Article 41 of the Constitution protects the family as the natural primary and fundamental unit group of society.
"The word natural clearly refers to the biological procreative functions of man and women creating a child."
Patsy McGarry, the Irish Times religious affairs correspondent, has described the campaign before Friday's referendum as divisive, even within the Church of Ireland.
He said: "The Anglicans are divided on the matter, some of their bishops have spoken out calling for a 'Yes' vote, and at least one has called for a 'No' vote, here in the Republic.
"So they haven't taken a formal position on the referendum at all except other than advising people to consult their own conscience on the matter," he told Premier.
Roman Catholic bishops have urged their congregations to be guided by church teaching on Friday, urging people to vote 'No'.
Irish voters are set to back the introduction of marriage equality by a margin of as much as two-to-one, according to the latest polls. Many observers believe it could be another example of the Catholic Church's waning influence on Irish society.
"One of the things that will be studied most clearly tomorrow, when the results are out is, to what extent the Catholic bishops have influenced the outcome; and the indications are that it won't be very profound and that their own moral authority has been deeply damaged by the abuse scandals of recent years," Patsy McGarry said.
Places where same-sex marriages are performed include Argentina, Belgium, Brazil, Canada, France, Iceland, Mexico, the Netherlands, New Zealand, Norway, Portugal, South Africa, Spain, Sweden, and, within the UK, England, Wales and Scotland, but not Northern Ireland.
Gay marriage is legal in many parts of the United States and the Supreme Court will soon rule on whether state-imposed bans are unconstitutional.
Listen to Pat Carey and John Waters debating Ireland's gay marriage referendum on Premier's News Hour with Des Busteed here:
